Pope Francis has declined to keep on the Vatican's conservative doctrine chief with whom he clashed over the issue of civilly remarried Catholics receiving Holy Communion.

The Vatican said Francis thanked Cardinal Gerhard Mueller for his service, and the pope is adopting the next in line in the Congregation for the Doctrine of the Faith, Jesuit Monsignor Luis Ferrer, to succeed Cardinal Mueller.

Francis could have kept on Cardinal Mueller, whose five-year term ends this weekend and who turns 70 in December, which is the normal retirement age for bishops.

However, they disagreed over Francis' opening to allowing Communion for civilly remarried Catholics, with Cardinal Mueller insisting they cannot, given church teaching on the indissolubility of marriage.

This was the second major shake-up this week, after Francis granted another Vatican hardliner, Cardinal George Pell, a leave of absence to return to his native Australia to face trial on sexual assault charges.

Gerhard Mueller and George Pell are two of the most powerful cardinals in the Vatican, after the Vatican secretary of state, Cardinal Pietro Parolin, and their absences are likely to create something of a power vacuum for the conservative wing in the Holy See hierarchy.

Emeritus Pope Benedict XVI had chosen Cardinal Mueller, a fellow German countryman, to lead the congregation in 2012.

Benedict took a hard line against clerical sex abuse as prefect of the congregation, and later as pope, defrocking hundreds of priests accused of raping and molesting children.

Benedict also insisted that bishops around the world send all cases of credibly accused priests to the congregation for processing, since bishops had for decades moved paedophiles from parish to parish rather than sanction or report them to police.

The sex abuse caseload during Cardinal Mueller's tenure piled up as more and more victims came forward from Latin America, Europe and beyond.

Francis confirmed last year there was a 2,000-case backlog, and he set about naming new officials in the congregation's discipline section to process the overload.

Cardinal Mueller's handling of the abuse portfolio came under fire from Marie Collins, an Irish survivor of abuse.

She resigned from Francis' sex abuse advisory commission in March in frustration over what she said was the congregation's "unacceptable" resistance to accepting the commission's advice on how to better respond to victims.